Method of closing a mould before at least partly filling a cavity of this mould with a solidifiable liquid

ABSTRACT

A method of closing a mold and a press therefore, whereby a first mold part is moved towards a second mold part by a first relatively large displacement via a mechanical non-fluid drive. The mold parts are then pressed against one another by a fluid system including a pneumatically driven hydraulic system to provide relative high mold pressures. Drive and follower pins are selectively coupled to the hydraulic system by a carousel for selectively coupling a mold part to the hydraulic system during the pressing portion of the cycle. The method and press are particularly suitable for encapsulating electrical components.

This is a division of application Ser. No. 07/710,264, filed Jun. 4,1991, now U.S. Pat. No. 5,252,053.

FIELD OF THE INVENTION

The invention relates to a method of closing a mold before at leastpartly filling a mold cavity with a solidifiable liquid, whereby a firstmold part is moved towards a second mold part parallel to a central axisand pressed against the second mold part by a hydraulic system, andsubsequently a mold cavity enclosed by the mold parts is filled with thesolidifiable liquid. The invention also relates to a press suitable forcarrying out this method. The invention also relates to a mold partsuitable for use in the press.

BACKGROUND OF THE INVENTION

A method of the kind described in the opening paragraph and a press forcarrying out this method are known from the German Patent 838.438 whichcorresponds to U.S. Pat. No. 2,657,429 In a first phase of this knownmethod, a first mold part is moved from an initial position parallel toa central axis to a second mold part by means of a liquid medium whichis pumped into a cylinder under a first pressure (for example, 35 at),upon which in a second phase the same liquid medium is brought under asecond, increased pressure (for example, 200 at) in order to press themold parts together. After the solidifiable liquid placed in the moldhas cured or solidified, the first mold part is returned to the initialposition by purely hydraulic means. A disadvantage of the known methodand press is that the quantity of hydraulic liquid medium which isdisplaced for opening and closing the mold parts is comparatively great,so that a comparatively large hydraulic pump is required with anassociated cooling device for cooling the liquid medium. The totalquantity of energy required for opening and closing the mold parts as aresult is also comparatively great.

SUMMARY OF THE INVENTION

The invention has for its object to provide a method by which the moldparts can be moved towards one another and pressed against one anotherwith a comparatively small quantity of hydraulic liquid medium having tobe pumped.

The method according to the invention is for this purpose characterizedin that a primary displacement parallel to the central axis in thedirection of the second mold part is carried out by the first mold partby means of a mechanical drive in a first displacement range, andsubsequently in an adjoining second displacement range a secondarydisplacement parallel to the central axis in the direction of the secondmold part is carried out purely by means of a pressurized fluid operatedsystem via actuators which after the primary displacement of the firstmold part are moved from an idle position to an operational position inwhich the mold parts are kept pressed against one another by theactuators after the secondary displacement has been completed by theactuators. The fluid operated system is suitable for exerting acomparatively great force during pressing together of the mold parts. Amechanical drive on the other hand is particularly suitable for movingthe mold parts. Thus a mold part may be displaced over a comparativelylarge distance with a comparatively small force thereby. The term"mechanical drive" is here understood to mean any direct drive of thefirst mold part in which no use is made of a fluid medium for thetransfer of forces during the displacement in the first displacementrange. During the primary displacement, the mold parts are moved up to asmall distance from one another by the mechanical drive. The quantity ofhydraulic liquid medium to be pumped in the method according to theinvention is comparatively small and is used during the secondarydisplacement for displacing the first mold part over the very smalldistance which causes the first mold part to lie against the second moldpart and for pressing together of the mold parts via the actuators.

The invention also has for its object to provide a press with which thedisadvantage of the known press is counteracted. According to theinvention, therefore, the press suitable for carrying out the method ischaracterized in that the press is provided with a mechanical drive bymeans of which the first mold part can be displaced parallel to thecentral axis and with a number of follower pins which cooperate with thefirst mold part and whose centerline extend parallel to the central axisand which can be coupled to a pressurized fluid operated system by meansof a number of drive pins arranged between the follower pins and thefluid operated system and functioning as actuators, which drive pins arecollectively rotatable about the central axis for alignment of thecenterlines of the follower and drive pins. At the start of the primarydisplacement, the drive pins are in the idle position and the followerpins are situated between the drive pins. After the primarydisplacement, the drive pins are collectively rotated about the centralaxis in order to align the centerlines of the follower and drive pins.The drive pins are then in the operational position. The fluid operatedsystem then exerts a force on the drive pins so that the drive pins aredisplaced during the secondary displacement, whereby the follower pinsare displaced and the first mold part is pressed against the second moldpart.

An embodiment of the press according to the invention is characterizedin that the follower pins have their bearings in a slide which isdisplaceable by means of the mechanical drive, while the follower pinscan be coupled to the fluid operated system at one side of the slide andcooperate with the first mold part at another side of the slide. Theresult of this is that the mechanical drive is not loaded when the moldparts are pressed against one another by means of the fluid system.Another advantage is that the mold parts can be easily exchanged uponthe switch-over to a different product to be formed in the mold cavity,while the slide and the follower pins supported in the slide need not beremoved from the press.

A further embodiment of the press according to the invention ischaracterized in that the follower pins are displaceable relative to oneanother and that the first mold part can be tilted about a pivot axiswhich is transverse to the central axis. As a result, the first moldpart is pressed against the second mold part with forces evenlydistributed over the mold part.

Another embodiment of the press according to the invention ischaracterized in that the press is provided with at least a stop pinwhich is situated between two follower pins and whose centerline extendsparallel to the central axis. The stop pin determines in a simple mannera change-over position of the first mold part in which the productformed in the mold cavity can be removed. The stop pin in thischange-over position lies against the drive pin which has been broughtinto a position intermediate between the idle position and theoperational position.

A yet further embodiment of the press according to the invention ischaracterized in that the drive pins have their bearings in a turretwhich is rotatable about the central axis. The result is that the drivepins are supported and rotated about the central axis in a simplemanner.

A still further embodiment of a press according to the invention ischaracterized in that the turret is provided with a ring gear which isin engagement with a pinnion and whose centerline coincides with thecentral axis. Such a turret drive is easy to manufacture andcomparatively cheap to purchase and maintain.

A yet further embodiment of the press according to the invention ischaracterized in that the mechanical drive comprises a threaded spindleand a nut which is displaceable over this threaded spindle, the nutbeing coupled to the first mold part. Such a mechanical drive isparticularly suitable for converting a rotary movement of, for example,an electric motor into a translatory movement, which is performed by thefirst mold part.

A still different embodiment of the press according to the invention ischaracterized in that a side of the first mold part facing away from thesecond mold part is provided with ribs which are situated opposite facesof the first mold part which can be pressed against the second moldpart. In such a mold part, the compression force supplied by the fluidsystem of the press is transmitted via the ribs to the faces which canbe pressed against the second mold part. A better transfer of forcestakes place by this than in the known press, in which the side facingaway from the second mold part is entirely flat. The second mold partmay also be provided with such ribs.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in more detail with reference to the drawing,in which

FIGS. 1, 2 and 3 diagrammatically show a press according to anembodiment of the invention suitable for carrying out the methodaccording to the invention, in which

FIG. 1 shows the press during a first displacement range,

FIG. 2 shows the press during the second displacement range, a actuatorsbeing moved into an operational position, and

FIG. 3 shows the press while the two mold parts are pressed against oneanother;

FIG. 4 shows partly in front elevation and partly in cross-section apress suitable for carrying out the method according to the invention;

FIG. 5 shows a side elevation of the press of FIG. 4;

FIG. 6 shows a first and a second mold part according to an embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Corresponding parts have been given the same reference numerals in thevarious Figures.

The FIGS. 1, 2 and 3 diagrammatically show in various phases a press 1according to the invention suitable for carrying out the methodaccording to one embodiment of the invention. The press 1 is providedwith a base plate 3 and an upper plate 7 which is connected to the baseplate 3 by means of four columns 5. One column of the three columns 5shown is represented in part only for the sake of clarity (the fourthcolumn is hidden). The columns 5 also serve as guides for a plate-shapedslide 9 which is movable along a central axis 13 which extends parallelto and central with respect to the centerlines 11 of the columns 5. Theslide 9 is provided with a first support block 15 and a first mold part17, while the upper plate 7 is provided with a second support block 19and a second mold part 21, which together with the first mold part 17encloses three mold cavities 22 (see FIGS. 3 and 6). The shape of themold cavities 22 depends on the products to be formed. The slide 9 canbe moved along the columns 5 by means of a mechanical drive whichcomprises a threaded spindle 23 and a nut 25 (FIG. 4) which can be movedalong the threaded spindle 23 and is connected to the slide 9. Themechanical drive will be explained in more detail with reference to FIG.4. The base plate 3 is provided with a pressurized fluid operated systemcomprising a combined pneumatic and hydraulic system 27 (only a portionof which is shown) which will also be explained with reference to FIG.4. Between the pneumatic hydraulic system 27 and the bottom of the slide9 are positioned four drive pins 29 which function as actuators andwhich, after alignment, can exert a pressure force on four follower pins31 which are slidably supported in the slide 9. The follower pins 31bear on the first support block 15 above the slide 9. The press 1 has aturret 33 which can rotate about the central axis 13 and which comprisesa bushing 35 in which the threaded spindle 23 is arranged and two discs37, 39 fastened to the bushing 35 and providing the bearings for thedrive pins 29 with sliding possibility. The disc 37 is provided with aring gear 41 at its circumference which cooperates with a pinion 43which is coupled to an electric motor 44 (see FIG. 5) via a shaft 42. Inthe position of the turret 33 shown in FIG. 1, the drive pins 29 are inan idle position. The first mold part 17 is at some distance from thesecond mold part 21 since the slide 9 has been moved in the directiontoward the base plate 3 by means of the mechanical drive (describedbelow in connection with FIGS. 4 and 5) until the stop pins 46 connectedto the slide bear with their bottom ends on the upper ends of the drivepins 29. The follower pins 31 project through openings 45 in the disc39. To move the mold parts 17, 21 against one another, the slide 9 ismoved (by a mechanical drive to be described) in connection with FIGS. 4and 5 below in the direction toward the second mold part 21 in a firstdisplacement range until the bottom ends of the follower pins 31 lie ina plane which, seen from the base plate 3, is higher than a plane inwhich the upper ends of the drive pins 29 are sinted. The first moldpart 17 is then at a small distance D (FIG. 2) from the second mold part21. The distance D between the mold parts 17, 21 may be equal to 0 mm ifthe first mold part 17 is moved against the second mold part 21 by themechanical drive. The position now occupied by the mold parts 17, 21corresponds to the end of the primary displacement of the slide 9.

In this position of the slide 9 it is possible to rotate the turret 33until the centerlines of the drive pins 29 are aligned in relation tothe centerlines of the follower pins 31. The drive pins 29 are then inthe operational position (see FIG. 2). In a second displacement range,the combined pneumatic hydraulic system 27 exerts an equal force on eachof the drive pins 29, so that the drive pins 29 are moved in thedirection toward the second mold part 21 until the upper ends of thedrive pins 29 and the lower ends of the follower pins 31 lie against oneanother and exert a force on the follower pins 31 which are movedthrough the slide 9. A force is thereby exerted on the first supportblock 15 which is moved in the direction toward the second mold part 21in the second displacement range until the mold part 17 connected to thesupport block 15 lies against the second mold part 21 (see FIG. 3). Thecombined pneumatic hydraulic system presses the first mold part 17against the second mold part 21 via the drive pins 29, the follower pins31, and the first support block 15. A solidifiable liquid is thenintroduced into the mold cavity, for example, by means of adiagrammatically shown multi-plunger device of a kind as described in,for example, U.S. Pat No. 4,723,899 incorporated by reference herein orGerman Patent 3336173 which corresponds to U.S. Pat. No. 4,632,653 andwhich patents are incorporated by reference herein which illustrateencapsulation of semiconductor chips. As a result, the term herein"filling of the mold cavity" includes at least partly filling the cavitywith a solidifiable liquid since the remainder of the cavity is occupiedby the component being encapsulated. The solidifiable liquid may be athermosetting or thermoplastic, usually electrically insulatingsynthetic material which is introduced into the mold cavity in liquidform and then cured or solidified. After filling of the mold cavity, thepressure of the pneumatic hydraulic system 27 is set for zero N/m², theturret 33 is turned into the idle position, and the slide 9 is moved inthe direction toward the base plate 3, upon which the formed product canbe removed from the mold cavity and the press 1 is ready for a newcycle. For the exchange of the mold parts, the turret 33 is turned to aposition in which both the follower pins 31 and the stop pins 46 canenter the openings 45 of the disc 39, and the slide 9 may be furthermoved in the direction toward the base plate 3.

FIGS. 4 and 5 show a press 2 of which the operational principlecorresponds to that of the press 1 diagrammatically shown in FIGS. 1, 2and 3.

The mechanical drive of the press 2 comprises a threaded spindle 23 towhich a gear 49 is fixed. The gear 49 is driven by a pinnion 53 coupledto an electric motor 51 via a shaft 52. The mechanical drive furthercomprises a nut 25 which is connected to the slide 9 via coupling rods54. When the threaded spindle 23 rotates, the nut 25 performs atranslation parallel to the central axis 13 in the upward or downwarddirection.

The pneumatic-hydraulic system 27 comprises a pneumatic pump 55, atransmission mechanism (not shown), a set of pneumatically drivenpistons (not shown) and four hydraulically driven pistons 59 which movein cylinder 57. Each hydraulic piston 59 has a corresponding pneumaticpiston. The pump 55 applies air pressure of comparatively low value (forexample, 3.5×10⁵ N/M²) against each of the pneumatically driven pistons(not shown), each piston having an effective piston surface area Atransverse the piston displacement direction. A hydraulic plunger (notshown) is fastened to each of the pneumatic pistons and has an effectivecross-sectional surface area B transverse the piston displacementdirection, the plunger being in contact with a liquid medium, forexample, oil which is in fluid communication with openings 61. Theplunger effective transverse surface area B is smaller than thepneumatic piston transverse area A by a factor X, so that the hydraulicpressure exerted by the plunger is greater than the air pressure drivingthe pneumatic piston by the same factor X. In this way it is possible toapply oil under a high pressure to the pistons 59 via connectionopenings 61 by means of the pneumatic pump 55 and the pneumatic pistonsso as to realize a compression force of 150.000N for each cylinder 57.The pistons 59 each have a portion 63 of reduced diameter which can bemoved through an opening 65 in a cover plate 67 of the base plate 3.During rotation of the turret 33, the drive pins 29 slide over the coverplate 67. The diameter of the drive pins 29 is greater than the diameterof the openings 65, so that the drive pins 29 cannot pass through theopenings 65. In the second displacement range and during pressing, theportions 63 of reduced diameter of the pistons 59 press against thedrive pins 29. The stroke of each piston 59 is approximately 5 mm and isdetermined by the distance D between the first and second mold parts 17,21, the distance between the lower ends of the follower pins 31 and theupper ends of the drive pins 29, which is approximately 1-2 mm, and thedistance between the lower ends of the drive pins and the ends of theportions 63 of reduced diameter, which is also 1-2 mm. To strip thepistons 59 from the drive pins after pressing, the oil pressure inopening 61 is reduced to zero N/m² and air pressure (for example,3.5×10⁵ N/m²) is applied to chambers 71 of the cylinders 57 via ducts(not shown) to drive pistons 59 toward the bottom of the drawing figure.

Each follower pin 31 at its upper end is provided with a bore 30 inwhich an auxiliary peg 73 is located, which is connected at one side 73Ato the follower pin 31 and at another side 73B carries a circularsupport plate 75 which bears on the slide 9 and by means of which thefollower pin 31 is suspended from the slide 9. Between the side 73A andthe side 73B, the diameter of the bore 30 is greater than the diameterof the auxiliary peg 73, and the auxiliary peg is capable of bendingunder mechanical load. The circular support plates 75 support hardenedplates 77 which are present in recesses 32 of the first support block15.

When the first mold part 17 and the second mold part 21 are pressedagainst one another, surfaces of the first mold part 17 are pressedagainst surfaces of the second mold part 21. In practice, owing totolerances, not all surfaces of the first mold part 17 will always hitagainst the surfaces of the second mold part 21 at the same moment. Ifthe mold part 17 can only be moved parallel to the central axis 13, theresult will be that a minimum required clamping force will be applied toonly a few surfaces of the mold parts. This results in that plastic moldmaterial will creep between surfaces of the two mold parts duringpressing, since these are insufficiently pressed against one another. Toprevent this, the press 2 is provided with a "floating" first mold part17. This means that the mold part 17 is movable not only parallel to thecentral axis 13, but is also tiltable about a pivot axis transverse tothe central axis 13. The moment the first mold part 17 is alreadylocally in contact with the other mold part 21 via a first follower pin31 with the maximum force F supplied by the pneumatic hydraulic system27, the other follower pins 31 will try to displace the support block 15and the first mold part 17 in the direction of the second mold part 21until the force by which each of the follower pins 31 presses is equalto the force F. The support block 15 and the first mold part 17 as aresult will tilt about the pivot axis until all follower pins 31 pressagainst the first mold part 17 via the support block 15 with the sameforce F. This is possible because the follower pins 31 can be movedindependently of one another and because the auxiliary pegs 73 arearranged in the follower pins 31 with bending capability, so that thefirst support block 15 which rests on the support plates 75 is tiltableabout the pivot axis.

FIG. 6 shows the first mold part 17 which is provided with ribs 81 at aside 79 remote from the second mold part 21, which ribs are situatedopposite faces 83 of the first mold part 17 which can be pressed againstthe second mold part 21. The pressure force supplied by the hydraulicsystem 27 of the press 2 is transmitted to the ribs 81 by the firstsupport block 15, the ribs passing the force on to the faces 83. The useof the mold part 17 depicted in FIG. 6 in combination with the tiltingpossibility of the mold part described above results in a very goodcompression of the first mold part 17 against the second mold part 21,so that no plastic mold material can enter between the surfaces of thetwo mold parts pressed together. It is possible to construct the firstmold part 17 in mirror-symmetrical form, so that in case of wear of theside facing the second mold part, the first mold part 17 may be turnedand the side 79 will face the second mold part 21. For the sake ofclarity, the mold parts 17, 21 are drawn in a position in which the moldparts 17, 21 do not lie against one another.

The mechanical drive may be realized by means of any known mechanism. Asan alternative to the threaded spindle and the nut, for example, alinear motor may be used. The drive pins 29 may also have their bearingsin a slide which is movable transverse to the central axis.

What is claimed is:
 1. A method of closing a mold comprising:displacinga first mold part toward, but not in contact with, a second mold partvia a non-fluid mechanical drive in a first primary displacement rangeparallel to a central axis; after the displacing, bringing into contactand pressing the first mold part against the second mold part in anadjoining second displacement range in a secondary displacement parallelto said axis via a pressurized fluid to form a mold cavity; and, duringsaid pressing at least partly filling the cavity with a solidifiablemoldable liquid; the bringing into contact and pressing of the firstmold part being carried out purely by said pressurized fluid viaactuators and at constant pressure, said pressing including, after theprimary displacement of the first mold part, moving the actuators froman idle position to an operational position in which the mold parts arekept pressed against one another by the actuators after the secondarydisplacement has been completed by the actuators.
 2. A method of moldingcomprising:displacing a first mold part toward, but not in contact with,a second mold part via a mechanical non-fluid operated drive in a firstprimary displacement range parallel to a central axis; after thedisplacing, bringing into contact and pressing the first mold partagainst the second mold part in an adjoining second displacement rangein a secondary displacement parallel to said axis via a pressurizedfluid at constant pressure to form a mold cavity; and filling the cavitywith a solidifiable moldable liquid during said pressing.
 3. The methodof claim 2 wherein the pressing step includes pneumatically operatinghydraulic means and causing the hydraulical means in response to thepneumatically operating to perform said pressing.